The present invention relates to a numerical-controlled machine tool for cutting a gear, such as a gear hobbing machine, a gear grinding machine or the like.
Generally, in this kind of machine tool, the synchronous relationships of the rotation of a cutter, such as a hob or the like, the rotation of a table carrying a workpiece and the vertical movement of the cutter are determined in accordance with the number of teeth and the tooth profile of the gear to be cut. In consequence, also in conventional numerical-controlled machine tools, command pulses are naturally distributed to respective drive shafts so that the synchronous relationships may be satisfied. In the prior art, however, the distribution pulses are produced by mounting a pulse generator on the shaft of the cutter and performing an operation of obtaining a unit amount of movement of each shaft which satisfies the above synchronous relationships, for each pulse generated by the rotation of the cutter; it is difficult to stop the vertical movement of a hob or change its speed, for example, during hobbing a helical gear. Accordingly, the prior art has the defect of severe limitations imposed on cutting conditions.